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9. UC-SLS Lecture 9 : Assembly : Operations and Data Types

9.1. A simple mov.S program

9.1.1. Setup

• create a directory mkdir mov; cd mov

• create and write mov.S below

• add a Makefile to automate assembling and linking

  • we are going run the commands by hand this time to highlight the details

• add our setup.gdb to make working in gdb easier

• normally you would want to track everything in git

CODE: asm - mov.S

	.intel_syntax noprefix
	.text
	
	.equ EXIT_SYSCALL_NR,60
	
	.global _start
	.type _start, @function	
_start:
	mov rax, 0b1000

	mov rax, EXIT_SYSCALL_NR
	mov rdi, 2
	syscall
	
	

9.1.2. Assemble mov.S into mov.o directly with assembler (as)

• -a produce listing to standard out

• we could add -g flag to add extra debugger information but lets skip it for now

9.1.2.1. mov.o is NOT an executable

9.1.2.2. What kind of file is is it?

9.1.2.3. Examine Symbol Table

9.1.3. Link mov.o to produce the binary mov with linker (ld)

• we don’t really have any other files to link

• simply need to have linker organize things as per os linker script (use ld -verbose to see the script )

  • note the syntax is very cryptic

9.1.3.1. recognize anything?

9.1.3.2. lets run it

9.1.3.3. We can use tools to convert the executable into a binary image

• objcopy is a very useful tool like objdump

  • let’s us convert the executable into various formats including raw binary

  • objcopy mov --output-target=binary mov.bin

9.1.4. gdb -tui mov -x setup.gdb

9.1.4.1. rebuild with more debug info -g

Debug

Once Loop Reflect

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8. SLS Lecture 8 : Writing some simple assembly programs

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10. SLS Lecture 10 : Assembly : Program Anatomy I